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Abstract

Background: Estimation of ventricular elastance at the aortic valve opening is fundamental for assessment of non-invasive end-systolic elastance (Ees). Despite conditional variability of time varying elastance (Et) property, the Et during isovolumic contraction (IVC) is less variable and highly adjustable, thus Et has been used to estimate Ees in a number of clinical studies. However, uncertain characteristics of Et due to morphological diversity hindered its application in single ventricular hearts (SV). We tested our hypothesis that Et in early systole is independent of ventricular morphology in SV patients.

Methods: During cardiac catheterization, a total of 78 pressure volume relationships were constructed from 26 children including 18 Fontan patients (right dominant: SRV n=8, left dominant: SLV n=10) and controls (n=8). Et curve, normalized both for Ees and time to Ees, was compared among groups at baseline, dobutamine infusion (DOB, 5 mcg/kg/min) and rapid supraventricular pacing.

Results: Shapes of Et in SRV and SLV at both baseline and DOB were similar, particularly during IVC and ejection phase (Figure). While Et was stable during pacing with additional 20-30 bpm to the baseline heart rate (HR), relaxation delay caused disturbance of Et in some patients at HR greater than 170 bpm. The slope ratio (α) of Et during ejection phase to that during IVC, which determines subtle variations of Et, was significantly correlated with ejection fraction (EF, R=.65, p<.01) and independent of ventricular type, preload and afterload.

Conclusion: Et properties in Fontan patients, both with SRV and SLV, highly resemble those in controls at baseline, with DOB, and physiological pacing during systole. Similar to structurally normal hearts, α can be predicted by EF. While impact of diastolic property on early systole should be accounted for in high HR patients, our results rationalized the utility of normalized Et that provides a fulcrum point to estimate Ees in Fontan circulation.